U.S. Pat. No. 4,844,639, issued to the same inventor of this application, discloses a writing instrument essentially comprising an outer body having a tapered forward portion in which a lead is retained by a pair of radially opposed fingers provided on the tapered forward portion for frictional engagement with a lead. However, since the lead 1 is movably held in between the two opposed fingers 15 of the outer body 10, the two fingers 15 after a long-time service of the writing instrument may lose their resilience due to fatigue failure, easily causing a downward slipping of the lead 1 from the two fingers due to a gravity of the lead itself when the press member 3 is downwardly depressed to release the clamping means such as the tightening ring 2 on the tapered portion 23 of the lower section 22 of the inner sleeve 20.
Meanwhile, the tightening ring 2 is reciprocatively held in the window 13 notched in the tapered forward portion 12 of the outer body 10. In order to provide an effective clamping of the lead 1 by the ring 2 and the tapered portion 23 of the inner sleeve 20, the ring 2 should have an enough length. Otherwise, a thinner ring 2 will soon be released from the tapered portion 23 to lose its clamping effect when the inner sleeve 20 is downwardly depressed, thereby being unable to clamp the lead to protrude the lead downwardly outwardly for writing use. However, if the ring 2 is made too long causing a long distance of the window 13 for the ring 2, a total length of the writing instrument will then be prolonged, possibly producing a poor appearance of the instrument.